Abstract: we report in situ transmission electron microscope dynamic observations of the growth of Cu2O islands during oxidation of (100)Cu thin films at ~900°C, which show that the oxide islands have an initially square shape that transits to a terraced pyramid morphology as growth proceeds. The surface topology obtained from ex situ AFM observation reveals that the terraced oxide pyramids have a hollow structure. A simple mechanical mechanism based on elastic-plastic deformation, instead of the kinetic/thermodynamic mechanism that is typically used to describe nanostructure evolution, is proposed to explain the formation of this completely new oxide structure.